1. Technical Field
The present invention relates to a projection system and information processing apparatus.
2. Related Art
In general, a projector is well known as an image projection apparatus.
There is also well known a projection system that includes a PC serving as an information processing apparatus that carries out shape correction or color-color-tone correction of an image source, a projector that projects an image corrected by the PC on a screen, and a USB cable serving as a data transmission path between the PC and the projector (see JP-A-2004-69996).
In the projection system, the image source inputted to the PC is image-processed by an image processing unit of the PC.
Examples of the image processing include trapezoid correction for correcting trapezoid distortion produced by a disposition between the projector and the screen, or color-color-tone correction for correcting unevenness of luminance or color produced by color characteristics of the projector. Image data that is image-processed by the PC is transmitted to the projector via the USB cable. When the image data is projected from the projector onto the screen, a predetermined image is displayed on the screen.
In the above-mentioned construction, since the image processing is carried out mainly on the PC, and the projector just projects the image data but does not carry out complex image processing, it is possible to simplify the construction of projector. In addition, since the PC has a graphic processing function, it is possible to carry out high-precision image correction without adding new functions to the PC.
In a case where an image source is a moving image, when the transmission rate of USB cable is low, it takes long time for single image data to be transmitted. Thus, the frame rate of image displayed by the projector becomes low, such that the moving image is not properly played. For instance, since the frame rate required for satisfactory playback of moving image is 30 frames/sec, it is not possible to transmit the whole image data using the USB2.0 cable. For instance, while a stable communication rate for the USB2.0 cable is about 240 Mbps, an image having XGA resolution (1024×768 dots) and color information of 30 bits/pixel has about a data amount of 25 Mbits. In this case, the image data can be transmitted only at a frame rate of 9 frames/sec. Even though the communication is made at a maximum communication rate of 480 Mbps in theory, the frame rate is just 18 frames/sec, which is not appropriate for playback of the moving image.
JP-A-2004-69996 discloses that the frame rate is maintained at an appropriate level by reducing a necessary amount of transmitted data by ‘differential data transmission of preceding image data’ (see paragraph 0048 of JP-A-2004-69996) In JP-A-2004-69996, the PC generates and transmits differential data to the projector, and the projector generates current-image frame data by synthesizing the preceding image and the differential data. The current-image frame data is projected from the projector onto the screen.
While JP-A-2004-69996 proposes that the transmission data is reduced by ‘differential data transmission’, it does not disclose a method of generating the ‘differential data’. In order to properly display images projected by a projector onto a screen, image data is required to be subject to shape correction, such as trapezoid correction, or color-color-tone correction, such as unevenness of color. At this time, it is a problem how to generate the differential data that is required to properly represent current-image frame data required for appropriate image projection by mean of the protector.